fix(worker): start_list_handler ehrlich machen, wenn keine App verbunden ist

ConnectedClientTracker zaehlt verbundene UI-Clients (WorkerHub.OnConnectedAsync/
OnDisconnectedAsync). StartListHandler prueft ihn vor dem Broadcast und liefert
bei 0 verbundenen Clients Requested=false plus Reason statt unbedingtem true.
Tool-Beschreibung und external-mcp.md an das reale Verhalten angepasst.

src/ClaudeDo.Worker/External/ListHandlerMcpTools.cs

@@ -7,32 +7,36 @@ using TaskStatus = ClaudeDo.Data.Models.TaskStatus;
 
 namespace ClaudeDo.Worker.External;
 
-public sealed record StartListHandlerResult(bool Requested, string ListId, string ListName, int TaskCount, IReadOnlyList<int> TaskNumbers);
+public sealed record StartListHandlerResult(bool Requested, string ListId, string ListName, int TaskCount, IReadOnlyList<int> TaskNumbers, string? Reason = null);
 
 // The "Let Claude handle it" button, reachable from outside the UI. The worker only broadcasts;
 // the App owns the ConPTY tile and creates the handler task exactly as the button does
 // (MissionControlViewModel.OpenMergeHelperConPtySessionAsync), so there is one code path for
-// starting a run, not two. Without a connected App nothing happens -- the result says so.
+// starting a run, not two. Without a connected App the broadcast has nobody to receive it, so
+// ConnectedClientTracker is checked first and Requested comes back false with a Reason instead of
+// an unconditional true.
 [McpServerToolType]
 public sealed class ListHandlerMcpTools
 {
     private readonly ListRepository _lists;
     private readonly TaskRepository _tasks;
     private readonly HubBroadcaster _broadcaster;
+    private readonly ConnectedClientTracker _clients;
 
-    public ListHandlerMcpTools(ListRepository lists, TaskRepository tasks, HubBroadcaster broadcaster)
+    public ListHandlerMcpTools(ListRepository lists, TaskRepository tasks, HubBroadcaster broadcaster, ConnectedClientTracker clients)
     {
         _lists = lists;
         _tasks = tasks;
         _broadcaster = broadcaster;
+        _clients = clients;
     }
 
     [McpServerTool, Description(
         "Start a list-handler run (\"Let Claude handle it\") for a list, exactly like the button in " +
         "Mission Control: the connected ClaudeDo App creates the handler task and opens the triage " +
         "ConPTY tile for the given tasks. taskIds defaults to every Idle, non-manual task of the list. " +
-        "Requires the App to be running and connected to this worker -- the worker only broadcasts " +
-        "the request. taskIds accept task numbers (#123 or bare 123).")]
+        "Requires the App to be running and connected to this worker -- if it isn't, Requested comes " +
+        "back false with a reason and nothing is started. taskIds accept task numbers (#123 or bare 123).")]
     public async Task<StartListHandlerResult> StartListHandler(
         [Description("The list to run the handler on.")] string listId,
         [Description("Tasks to hand to the run, in the order to triage them. Omit for all Idle, non-manual tasks of the list.")] IReadOnlyList<string>? taskIds = null,
@@ -65,8 +69,15 @@ public sealed class ListHandlerMcpTools
         if (chosen.Count == 0)
             throw new InvalidOperationException($"No tasks to hand to the list handler for {list.Name}.");
 
+        var numbers = chosen.Select(t => t.Number).ToList();
+        if (!_clients.AnyConnected)
+        {
+            return new StartListHandlerResult(false, listId, list.Name, chosen.Count, numbers,
+                "No ClaudeDo App is connected to this worker, so the request could not be delivered. Open the app and retry.");
+        }
+
         var ids = chosen.Select(t => t.Id).ToList();
         await _broadcaster.ListHandlerStartRequested(listId, ids);
-        return new StartListHandlerResult(true, listId, list.Name, ids.Count, chosen.Select(t => t.Number).ToList());
+        return new StartListHandlerResult(true, listId, list.Name, ids.Count, numbers);
     }
 }